Fining heat absorbing reduced glasses



Patented July 30, 1935 FINING HEAT ABSORBING REDUCED GLASSES Robert H.Dalton, Corning, N. Y., assignor to Corning Glass Works, Corning, N. Y.,a corporation of New York No Drawing.

Original application July 30, 1932,

Serial No. 627,102. Divided and this application January 15, 1934,Serial No. 706,777

Claims.

This invention relates to the fining of glass and has for its object thefining of glass melts which have been reduced by the addition of batchestherefor of reducing agents such as car- 5 bon, carbonaceous materials,zinc dust, and the like, herein referred to as reduced glasses.

The above and other objects may be attained by practicing my inventionwhich embodies among its features the addition to such glass batches ofa small amount of a substance containing bromine.

Glasses reduced by the addition of carbon or carbonaceous materials arepractically never perfectly fined and there has long been a need formeans for fining such glasses. Arsenic which is ordinarily used as afining agent is obviously without value in reduced glasses, because thesuccessful use of arsenic for this purpose requires oxidizing conditionssuch as the presence of a nitrate or the use of the higher oxide ofarsenic. Moreover, it is sometimes difiicult to obtain uniform reductionin glasses reduced by carbonaceous materials because the carbon,although initially uniformly distributed throughout the batch, does notreadily dissolve in the glass when the batch is melted but tends tosegregate and rise to the top of the melt where it may be burned off orcause over-reduction while the bottom part of the melt is insufiicientlyreduced.

I have discovered that substances containing bromine, such as bromides,bromates, and the like, are very efficient fining agents when added insmall quantities to batches for reduced glasses. I have further foundthat substances containing bromine are of themselves mild reducingagents and inasmuch as they, for the most part, seem to dissolve readilyin glass they tend to promote more uniform reduction throughout the meltthan is possible through the use of carbon alone. On account of theirmild action they do not tend to produce the so-called carbon ambercoloration and the use of an excessive amount, therefore, has no illefiect, although on account of expense I prefer to use not more than 2%,which I have found to be ample for fining purposes.

My invention is particularly valuable in fining the so-called heatabsorbing glasses which contain ferrous iron and must be melted withstrong reduction. Heretofore, it has been practically impossible to finesuch glasses and at the same time to maintain the proper heat absorbingeificiency. The following batches with the results of their melting willillustrate the application of my invention to heat absorbing glasses:

Sand 335 335 Sodium carbonate 80 Borax 125 Ferric oxide l0 10 Carbon MPotassium bromide 10 Degree of fining Fine bubbles. N o bub- 98. Heattransmission in 2 mm. thickness... 6. 3% 5. 9%

Glass A, which contained carbon but no bromine, is an example of a priorheat absorbing glass. It was reduced as is shown by the low heattransmission but was not fined.

Glass B is an example of the use of a bromine containing material inconjunction with a reducing agent in accordance with my invention. Itwas perfectly fined and its heat transmission, which is slightly lowerthan that of glass A, apparently indicates that bromine materials in noway interfere with the reducing action of carbon. In fact, in theexample cited the results are slightly better with bromide and carbonthan with carbon alone.

Low expansion borosilicate heat absorbing glasses are particularlydifficult to fine on account of their high melting points and relativelyhigh viscosities at melting temperatures. By the addition of 1 to 2% ofa material containing bromine to such glasses, I am able to fine themand still retain their heat absorbing efliciency.

I have found also that chlorine containing materials are not asefficient fining agents as materials containing bromine and, whenintroduced into glasses in amount comparable to the amount of brominematerial which I have found necessary to cause fining, the chlorinematerial tends to produce opal glasses, particularly in the case of lowexpansion borosilicates. I, therefore, make no claim to the use ofchlorine materials for this purpose.

In the following claims the terms reduced glass and reduced glassesrefer to glasses which are melted under reducing conditions, or

to glasses which result from melting batches that contain a reducingagent such as carbon or carbonaceous materials and in this connectionbromine materials are considered to be reducing agents.

This application is a division of my original application filed July 30,1932, Sr. No. 627,102.

What I claim is:

1. The method of fining reduced glasses which includes adding to thebatches therefor a small amount of a bromine containing material and areducing agent. a

2. The method of fining reduced glasses whiclfr

